1. Field of the Invention
This invention relates to a subcode graphics reproduction control apparatus designed to perform operations of generating a graphics video signal from a subcode signal obtained through playback of a recording medium, mixing the generated signal with a video signal input from outside, and supplying the mixed signal to an image display device.
2. Description of Background Information
In digital audio discs such as the Compact Disc (CD), the subcode is recorded in addition to digital audio signals recorded as the main code. The structure of the subcode is standardized as described below. The subcode contained in each frame of the main code is made up of 8 bits, and a bit group constituting one subcode block is divided into 8 channels of P, Q, R, S, T, U, V and W. Among these channels, the channel Q bit includes time information corresponding to a track length from the start position of a program area of the CD to a specified position of each information data recorded therein, and carries address time data available as positional data indicating the recording position. The channel P bit carries data including information of the pause between recorded music pieces. In a system where image information is recorded and reproduced in the form of the subcode as shown in FIG. 1, one symbol in the data corresponding to the image information consists of 6 bits from channel R to channel W, and 98 symbols are treated as one block. The first two of these 98 symbols are used as a synchronizing signal, and 24 symbols obtained by dividing the remaining 96 symbols to equal portions are treated as the minimum unit (PACK), and constitute one image processing instruction.
As shown in FIG. 2, each PACK has MODE and ITEM each comprising 3 bits, and the MODE and ITEM indicate a mode of the PACK. For instance ZERO mode is designated when MODE=000 and ITEM=000 and TV graphics mode is designated when MODE=000 and ITEM=001. Symbol 1 is set as INSTRUCTION, while symbols 4 to 19 are data fields. The INSTRUCTION defines characteristics of the data fields. The symbols 2 and 3 indicate a Q parity (Parity Q0, Q1), and are used to correct errors in symbol 0 or 1. The symbols 20 through 23 indicates a P parity (PARITY P0 through P3), and are used to correct errors in symbols 0 through 19.
In the TV graphics mode, the configuration of a TV screen is set up based on the unit designated as FONT. As shown in FIG. 3, one FONT comprises 6 pixels in the horizontal direction (column) and 12 pixels in the vertical direction (row), and a pixel is a minimal picture element which can be displayed. A SCREEN area which can be actually displayed on the TV screen is formed by 48 (in the horizontal direction).times.16 (in the vertical direction) FONTs, and an area surrounding the SCREEN area is called BORDER area. A display memory for the TV screen consists of 50 (in the horizontal direction).times.18 (in the vertical) FONTs, so that the total size is larger than that of the SCREEN area by one font in the upper and lower directions and in the right and left directions. Also a pointer is defined to realize soft scrolling. The horizontal screen pointer PH indicates a horizontal shift rate to horizontally displace all pixel data in the display memory, while the vertical screen pointer PV indicates a vertical shift rate to vertically displace all pixel data in the display memory.
For the TV graphics mode, instructions are defined as shown in FIG. 5. In the case of instruction 1 which is a display-memory preset instruction, the data area in the PACK has the configuration as shown in FIG. 6. All fonts in the display memory are preset to a color number specified by COLOR in symbol 4, and pointers PH and PV are reset to 0. In the case of instruction 2 which is a border-preset instruction, the data area in the PACK has the configuration as shown in FIG. 7, and the border area is preset to a color number specified by COLOR in symbol 4 for color. In the case of instruction 6 which is an instruction for writing foreground/background FONT, the data area in the PACK has the configuration as shown in FIG. 8. This command is to write font data in symbols 8 to 19 (color number data) at an address position defined by the ROW specified in symbol 6 and the COLUMN specified in symbol 7. In FIG. 8, Y indicates the top-left pixel in the FONT, while Z indicates the bottom right pixel in the font. A color having a color number specified by COLOR0 in symbol 4 is written as a foreground color for pixels having the font data of "0" and a color having a color number specified by COLOR1 in symbol 5 is written as a foreground color for pixels having the font data of "1", in both cases, in bit planes 0 to 3 of the display memory.
In the case of instruction 20 which is a scroll screen instruction with presetting, the data area in the PACK has the configuration as shown in FIG. 9. COPH in symbol 5 indicates the movement of font data in the display memory in the horizontal direction, while COPV in symbol 6 indicates the movement of font data in the display memory in the vertical direction.
In the case of instruction 24 which is a scroll screen instruction with copying, the data area in the PACK has the configuration as shown in FIG. 10. COPH in symbol 5 indicates the movement of font data in the display memory in the horizontal direction, while COPV in symbol 6 indicates the movement of font data in the display memory in the vertical direction.
In the case of instruction 30 which is a load CLUT COLOR 0 to 7 instruction, the data area in the PACK has the configuration as shown in FIG. 11. This command specifies 8 colors in the first half of the color look-up table which indicates which color among 16 colors corresponds to each of the aforesaid color numbers. In symbols 4 to 19, graphics RGB data specified by COLOR-0 to COLOR-7 is set, using 2 symbols for one color. In the case of instruction 31 which is a load CLUT COLOR 8 to 15 instruction, COLOR-8 to COLOR-15 are set, using 2 symbols for one color, to specify 8 colors in the second half of the color look-up table. The mixing of colors for each color number is such that the red color comprises 4 bits of channels R to U in an even number symbol assigned to one color number, the green color comprises 2 bits of the subsequent channels V and W and other 2 bits of the channels R and S in the next odd number symbol, and the blue color comprises 4 bits of the furthermore subsequent channels T to W. Since the gray scale is 2.sup.4 =16 levels for each of three colors R, G, and B, so that 16.sup.3 =4096 ways of color mixing are possible. In the gray scale, "0000" indicates the darkest state, and "1111" indicates the brightest state.
The instruction 38, which is an exclusive-or font instruction, is used to limit the color in a FONT written with two colors or one color according to the preset instruction or the foreground/background font write-in instruction up to 16 colors.
In the case of instruction 28 which is a transparency-set command, the data area in the PACK has the configuration as shown in FIG. 12. This command is used to set a mixing ratio when graphics image is mixed with moving pictures, and the mixing ratio is specified in the transparency look-up table indicating transparency of each of 16 colors defined in the color look-up table with TRANS-0 to TRANS-15 in symbols 4 to 19. With this instruction, the transparency of the color in all pixels can be specified with 6 bits to any of 64 stages, in which "000000" indicating the least transparent state and "111111" indicating the most transparent state.
Standards for subcode as described above are described in detail, for instance, in October, 1986 issue of "JAS Journal", a magazine published by the Japan Audio Association.
The subcode graphics reproduction control apparatus which generates a video signal indicating TV graphics image from subcode signals of TV graphics mode output from a disc player based on the subcode provided as described above is disclosed, for instance, in Japanese Patent Laid Open Publication No. 1-256060, and is well known. Also this type of apparatus has a superimposing function to synthesize graphics with moving pictures by means of mixing video signals output from a VTR (Video Tape Recorder) or a video disc player and indicating a moving picture or a still picture (simply called moving picture video signal hereinafter) with graphics video signals.
In prior art-based subcode graphics reproduction control apparatuses as described above, however, there has been an inconvenience that the fade operation cannot be carried out unless the attenuation degree is manually changed by the user.